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Conflict emerges over value of handwashing

Ottawa, Ont.
CMAJ

There’s no evidence that good hand hygiene practices prevent influenza transmission, according to a Council of Canadian Academies report commissioned by the Public Health Agency of Canada (PHAC).

But N95 particulate respirator-type masks are a proven "final layer of protection" against even the smallest viral particles of influenza, according to Influenza Transmission and the Role of Personal Protective Respiratory Equipment: An Assessment of the Evidence, a report prepared by an expert panel on influenza and personal protective respiratory equipment chaired by Dr. Donald Low, microbiologist-in-chief at Mount Sinai Hospital in Toronto, Ontario (www.scienceadvice.ca/documents/(2007-12-19)_Influenza_PPRE_Final_Report.pdf).

Despite those 2007 findings, PHAC still recommends handwashing as the primary preventive measure against flu transmission. The agency also states on its website that there is no evidence that wearing masks "will prevent the spread of infection in the general population. Improper use of masks may in fact increase the risk of infection."

Moreover, PHAC states in an email to CMAJ that "there is substantial evidence to support hand hygiene as a basic premise of infection prevention and control measures." The agency also indicated that its hand hygiene recommendations are based on a combination of expert opinion and evidence, including a recent Cochrane Collaboration systematic review (BMJ 2009;339:b3675).

But the contradictory evidence and recommendations on preventive measures and other pandemic (H1N1) 2009 issues leaves Canadian doctors at a loss as to the best advice to provide patients, says College of Family Physicians of Canada President Dr. Sarah Kredentser.

"The average family physician is confused and that’s partly because there is a lot of conflicting evidence, and things change day by day," Kredentser says, adding that there’s a need for the experts to get the information right and then get it out quickly to family physicians. To that end, the college is now working with PHAC, the Canadian Medical Association and other bodies to craft a one-page influenza guideline for physicians to use in the community.

View larger version (48K): [in this window] [in a new window]   Prominent microbiologist Dr. Donald Low argues that the Public Health Agency of Canada’s hand hygiene recommendations "are not evidence-based.". Image courtesy of ©2009 Jupiterimages Corp.

According to the Council of Canadian Academies report, though, there’s no conflicting advice regarding hand-washing or the use of N95 respirators.

Low argues that the PHAC’s hand hygiene recommendations "are not evidence-based." Noting that research on influenza transmission is limited, he adds that in the absence of adequate evidence, recommendations are often just "expert opinion."

Handwashing is based on practical, rather than scientific, considerations, he says. It is "a simple thing to do and it may protect you from some other illnesses."

But current evidence shows that influenza is transmitted primarily at a short range of 1–2 metres by inhaling particles from an infected person ("inhalation transmission"), although the virus can survive on surfaces and, theoretically, transmission can occur from contaminated surfaces to hands ("contact transmission"), according to the report, which was drafted in 2007 by 13 senior academic and clinical physicians, nurses and a judge. The expert panel, which examined 128 sources of evidence, was struck by the Council of Canadian Academies in response to a request from PHAC. The council was established in 2005 with a $30-million founding grant from the government of Canada to provide independent assessments of scientific issues for governments and other bodies.

Low explains that receptors for the virus are located farther back in the respiratory tract than those for rhinoviruses (colds). It is more difficult for viral particles to reach the pharynx, trachea, bronchi and alveoli — where influenza receptors are found — from a contaminated hand touched to the mouth or nose. The particles can more readily reach the sites if they are inhaled.

"Every time you talk, laugh, cough, sneeze, you’re generating particles that are coming out of your mouth that are various sizes," Low says. "Ballistic" particles more than 100 microns in diameter fall to the ground. But smaller particles ranging from 0.1 to 100 microns stay in the air from seconds to days, depending on humidity, airflow and ultraviolet light. These particles can be inhaled deeply into the respiratory tract, with smaller ones capable of reaching the tracheobronchial and alveolar tissues.

In practice, studies show the greatest risk is within one metre, Low adds. "Whether someone is infectious will vary [with] the amount of virus. There’s a huge dilutional factor right away as soon as you get away from the person infected."

Surgical masks — designed to protect patients from surgeons — provide some protection against contact and inhalation transmission, but allow air in the sides and do not meet an established standard, Low explains.

N95 masks, however, do meet the test. Created to protect workers in the construction industry from breathing in particulates and widely available in hardware stores, they must meet standards set by the US National Institute for Occupational Safety and Health. They fit tightly on the face and block particles as small as 0.1 micron.

While PHAC states on its website that it does not recommend that healthy people wear masks as they go about their daily lives, Low says N95 masks have a role in protecting the public. "If you had somebody at home with influenza, wearing an N95 mask would be very appropriate."

Canada’s Chief Public Health Officer, Dr. David Butler-Jones, states on PHAC’s website, though, that it can be easy to get a false sense of security from wearing the mask.

Low counters: "I don’t know where the false sense of security would come from."

Footnotes

Previously published at www.cmaj.ca

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This Article Figures Only Full Text (PDF) All Versions of this Article: cmaj.109-3066v1 181/10/667    most recent Submit a response View responses Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Brown, C. Articles by Kondro, W. PubMed PubMed Citation Articles by Brown, C. Articles by Kondro, W. Related Collections Other public health Influenza

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